Propagation of action potentials depends on the excitable membrane properties of individual cells and the interconnections of these cells into an electrical syncytium. The pattern of action potential propagation and therefore the excitation sequence of the heart depends on the regional variation of these parameters. In the vertebrate heart there has been considerable difficulty in measuring either membrane properties or parameters of interconnection due to the complex three dimensional structure. We propose to study the membrane properties and the wavefront propagation of the heart of the tunicate, Ciona Intestinalis, because of its unique structure of a regular two dimensional sheet of cardiac cells. We have already developed a method for simulating action potential propagation in an inhomogeneous sheet of electrically coupled excitable cells. With data from the tunicate heart, we can make this model more realistic and testable, and then apply it to further our understanding of the interaction of excitable membrane properties and intercellular connections in the propagation of action potentials in more complex vertebrate heart tissue.